It is desirable to regulate the operating temperatures of the engine and other heat generating components in a automobile or other vehicle. A heat exchanger is used to help regulate the operating temperatures by removing heat. Heat is removed by forcing air across the heat exchanger using a fan when the vehicle is stationary and using ram air when the vehicle is moving. The ram air is typically funneled to the heat exchanger via an air duct. In older vehicles, the duct system utilized an open mesh front grill structure through which air passed directly to the heat exchanger. In modem vehicles, however, an open front grill structure for ram air is deminimus or nonexistent because of aerodynamic and aesthetic design considerations. As a result, the opening for the air inlet duct is located behind the front bumper of the vehicle.
The exact position of the inlet to the duct varies from vehicle to vehicle and also varies within a vehicle family depending upon the bumper and accessories used. At the inlet, air velocity varies dramatically in the vertical direction because of the exterior shape of the vehicle and because of the position of the inlet opening, but is more nearly constant in the horizontal direction. This gives rise to a much larger volume flow rate entering the lower part of the inlet opening which biases the air flow toward the lower portion of the heat exchanger. It is possible for two thirds of the air flow to flow to the bottom one third of the heat exchanger leaving only one third of the air flow for the top two thirds of the heat exchanger which is inefficient and undesirable. This air distribution causes uneven cooling in a typical heat exchanger wherein the coolant travels horizontally. Accordingly, it will be appreciated that it would be highly desirable to have an air inlet duct that evenly distributes air flow to the both the top and bottom portions of the heat exchanger for efficient and effective cooling. It is also desirable to have an air inlet duct that evenly divides air flow regardless of the exterior shape of the vehicle or position or configuration of the front bumper.